The invention relates to inkjet printers. More specifically, the invention relates to the transmission of swath data from a host to a printer.
A typical tri-color printer includes a first pen for printing cyan-colored dots, a second pen for printing magenta-colored dots, and a third pen for printing yellow-colored dots. Each pen includes a plurality of vertically-oriented nozzles. When a nozzle is thermally actuated, it lays down a colored dot on a sheet of paper. During printing, the pens are moved across the sheet in tandem so as to allow multiple dot colors to be laid down. Each time the print head is moved across the sheet, a swath of dots is printed.
The nozzles are actuated according to swath data. Each bit of the swath data indicates whether a nozzle should be actuated at a specific position along the sheet.
The swath data is usually generated by a host, such as a personal computer, and transmitted to the printer. When received by the printer, the swath data is stored in a random access memory (“RAM”) buffer. For a single pen having 100 nozzles and a 300 dot per inch (“dpi”) printing resolution, a full 8″ swath would include 240 K pixels. Storing data representing the full swath would require 30 K bytes of RAM. For higher resolutions, taller swaths, more pens and more nozzles per pen (for example, some pens have two columns of nozzles), memory requirements would be much greater.
To reduce the amount of data that is transmitted, the swath data may be compressed by the host, transmitted in compressed form, and decompressed by the printer. Decompression is performed on the fly, and uncompressed swath data is stored in the RAM buffer and used to actuate the nozzles during printing.
The typical inkjet printer includes a printed circuit board, an Application Specific Integrated Circuit (“ASIC”) containing a printer controller, and a separate integrated circuit including the buffer. Among its functions, the printer controller decompresses the swath data and uses the uncompressed swath data to actuate the nozzles.
Each integrated circuit adds to the cost of the printer. Each integrated circuit has a separate package, each package is mounted to the circuit board, and each package takes up valuable real estate on the circuit board. Moreover, the buffer integrated circuit is a memory chip of a standard size, which is usually much larger than needed for buffering the uncompressed swath data.
It would be desirable to embed the buffer in the printer controller ASIC. Embedding the buffer would reduce the costs associated with an extra integrated circuit package.
However, embedding the buffer can increase the size and cost of the printer controller ASIC. Many printer controller ASICs are already core limited. Increasing the size of a core-limited ASIC would require die size of the ASIC to be increased. A significant increase in the die size would increase the cost of the printer controller ASIC.
It is an objective of the invention to reduce the buffer size in order to embed the buffer without significantly increasing the die size of the printer controller ASIC.